Method of and apparatus for screening pulp



April 15, 1930. A] J. HAUG N 1,755,162

METHOD OF AND APPARATUS FOR SCREENING PULP Filed Dec/'20, 1928 5 Sheets-Sheet 1 Q N m s: N INVEZZ'OR 2 5 5r ,47-T0RNE' April 15, 1930. A. J. HAUG 1,755,162

' METHOD OF AND APPARATUS FOR SCREENING PULP I Filed Dec. 20, 1928 3 She'et-sSheet 2 /N l/ENTOE.

" A TTORNEY April 15, 1930. A. J. HAUG 1,755,162

METHOD OF AND APPARATUS FOR SCREENING PULP Filed Dec. 20, 1928 3 Sheets-Sheet 3 g, I //VII/EN7 OR.' t.

Patented Apr. 15, 1930 ANTON J. HAU G, OF NASHUA, NEW HAMPSHIRE METHOD OF AND APPARATUS FOR SCREENING PULP A Application filed December 20, 1928. Serial No. 327,390.

This invention relates to the screening of pulp for the purpose of separating the good fibre suitable for delivery to the paper making wire or cylinder from the slivers and coarser materials.

Heretofore the results obtainable with the flat type of pulp screens have been superior from a quality standpoint to those produced by pulp screening machines of the centrifugal type. This is particularly true when the machines are used to grade pulp or stock. Machines of the latter type, however, are greatly superior to the former respects, especially in capacity. With these considerations in mind the present invention has for its general object to improve both the processes 'of and apparatus for screening pulp with a view to combining the advantages of both typesof screens.

available those of the general construction shown in my prior Patents Nos. 1,533,410

ranted April 14, 1925, and 1,551,953, granted ept. 1, 1925, have been found to give especially favorable results because of their large capacity, low power consumption and great reliability. It is, therefore, an important ob- .ject of this invention to devise a system in which machines of this type can be used to i so produce a grading of pulp or paper stock that will compare favorably with the results obtainable with flat screens. The invention also involves improvements in the type of screening machine shown in my patents above designated to increase the screening capacity per machine and to reduce the power consumption per ton of screened stock.

The nature of the invention will be readily understood from the following descrip- 4 tion when read in connection with the accompanying drawings, and the'novel features will be particularly pointed out in the appended claims.

In the drawings,

Figure 1 is a perspective view illustrating -a pulp screening system organized in accordance with this invention;

Fig. 2 is a longitudinal vertical sectional view through one of the machines shown in Fig. 1;

in some other Of the centrifugal screens commercially 7 means are Fig. 3 is an end view of the adjusting mechanism for the scoop or scraper used in the machine shown in Fig. 2; I

Fig. 4 is a vertical, transverse, sectional 'view through the scraper and the adjacent tailings conduit; and

Figs. 5 to 8, inclusive, are diagrammatic views illustrating systems embodying this invention but using other pulp screening machines.

According to the preferred method of practicing the process provided by this invention, a stream of pulp to be screened is flowed continuously through a series of pulp screening machines, and each machine takes a part of the fine stock from this stream but passes on to the next machine a suflicient proportion of the good stock, together with the slivers and coarser materials, (usually referred to as tailings) to maintain the consistency of the unscreened stock approximately unchanged as it passes from one machine to the next.

The apparatus'or system illustrated in Fig. 1 comprises a series of pulp screening machines each constructed, arranged and operated substantially as shown and described in my prior Patent No. 1,551,953 previously mentioned. One of these machines is shown in considerable-detail in Fig. 2. Referring to this figure it will be seen that the machine there'illustrated comprises a casing including end pieces 2 and 3 and a shell 4. Mounted 'in this casing is a rotary screening drum 5 ,of approximately cylindrical form which is bolted to an end piece 6 secured fast on the end of a horizontal shaft 7. This shaft is supported in bearings 8-8 and carries a pulley 9 by means of which it may be belted to any convenient source of power. The screening drum and its supporting and operating designed to permit a very rapid rotation of the screen so that a considerable centrifugal force will be created by the motion of the drum on the stock closely adjacent to it. 7

The pulp to be screened is conducted into the drum 5 through an intake spout 10 and the screened stock is discharged from the casing 4 through a conduit or spout 12, Fig. 1, which leads into a box 13 equipped with a lar to that disclosed in rotation of the drum creates a very substantial centrifugal force in the stock adjacent to the screen, and this force urges the stock through the screen. Usually the pulp is flowed slowly into the intake chute 10 from a head box, a portion of which is shown at 11, and the centrifugal force created by the screen adds to the hydraulic head'so that the level of the stock as it flows over the weir in the discharge or outlet box 13 may be, and usually is, higher than the of the supply. The slivers and coarser materials which cannot pass through the screen collect on its inner surface and are moved alongthis surface toward the tailings outlet by inclined scrapers 14. This results in delivering the tailings to the annular'head 6 to which the screen is secured,

andas the tailings are revolved, partly by their contact with this member 6 and partly due also'to the motion previously imparted to them by the screen, they are brought into engagement with a scoop or scraper 15 which directs them into a tailings discharge conduit.

16 that is located axially in and extends lonings are discharged from this conduit into a box 17 equipped with'an adjustable weir 18' which serves to apply a certain amount of back pressureorhydraulic head to the tallings.

As above stated, this machine is very s mimy Patent No. 1,551,- 953 but differs from it particularly in the arrangement of the parts which handle the stock that does not flow through the screening surface. That is, in the machine shown the outlet for the stock flowing more or'less axially through the drum and out of the tailings conduit 16 is made relatively large and comparatively unobstructed so that a .relatively free passage is providedfor the fiowof pulp through and out of the drum 5 but past the screening surface. .-In order to regulate or control the proportion of stock which will;

thus be discharged fromsthe screening drum without being subjected. to the screening action, the scoop or scraper 15 is made adjustable. end of a rod or rockshaftj20 which extends longitudinally through the upper part of the conduit 16 and through the box 17 to a point outside the casing. At this point a segment 21, Figs. 2 and 3, is secured fast to therock shaft and a Worm 22 is arranged to mesh with this segment, the worm being mounted on a shaft 23 carrying a hand wheel 24. A

pointer 25 is secured to the segment 21 and is mounted to swing across a dial plate 26 which is graduated to indicate the angular position ordegree of openin or closing of the scoop 15. As shown in Fig. 4 the scoop is mountto the machine is caused to As shown it is secured fast on the inner ed at one end of an opening 27 formed in the mg not only to adjust the scoop but alsofto I hold it positively in its adjusted position.

The systemshown in Fig. '1 includes four machines indicated at A, B, C and D, respectively, each of approximately the construction shown in Fig.2. It will be observed that the tailings discharge box 17 of each machine is connected b a trough or conduit 28 with the intake 11 o the series. The stock to be screened is deliv ered to the intake spout 11 of the first machine A, and the scoop or scraper 15 of this machine is so adjusted thata part only of the good stock is taken out of the stream of pulp as it flows through this machine, the fine stock so removed. from the stream beingdischar ed through the conduit 12 for this particu ar machine. A very large part of the-good stock in the stream of pulp is caused to pass through this machine with the tailings and is discharged from the machine through the tailings conduit 16, headbox 17, and trough 28 into the pulp intake 11 of the second machine gi'tudinally through the screen. The tail- 1n the machine A are repeated. That-1s, a

ere the operations which have occurred part of the goodstock screen of the machine B and is taken out of the stream of pulp and discharged through the outlet 12 for the good stock. Here again a large proportion of the good stock delivered ass along, with the tailings sus ended in it, ings outletf16, ox 17, and trough 29 to the pulp intake of the next machine 0. The same action is repeated in the third machine of the series, the1 volume of unscreened pulp, how ever, growing smaller, and a relatively small the next succeeding machine in v passes through the rough the tail volume is delivered to the final machine D. I

vThis machine is adjusted to take practically all of the good pulp out of the stream and to discharge from the tailings outlet only the splinters and coarse constituents which are unfit to deliver to the papermaking wire or cylinder. These tailings later may be treated of them. a v

The pulp delivered to the first machine in in arefiner or the like, to make good pulp out the series will, in atypical instance, have a' conslstency of approximately .5 or-.6 of1%.

That 1s, approximately one-half of one per? cent of the weight of the entire mixture consistsof dry solids.

The solid constituents are composed chiefly of relatively fine fibre, and

a very much smaller pro ortion' of coarse materials. 'As the pulp ows through the first machine a very considerable part-of this fine stock, that is,

the fibre with the liquid in which it is suspended, is urged through, the screening surface by the centrifugal force. created by the motion of the screen itself, this movement of the fine stock taking place against the head ofscreened stock which surrounds the screening drum, as in my patents above referred to. At the same time a very substantial part of the fine pulp or good stock is forced longitudinally through the drum by the head of incoming stock so rapidly that it has no opportunity to reach the screening surface and it is discharged through the tailings outlet, carrying with it the coarser constituents or tailings which have been rejected by the screen. The rotary motion of the screen is utilized in producing this discharge of the mixture of good stock and tailings from the machine audits delivery to the next succeeding machine, since it serves to raise the discharged mixture to such a level that it will flow by gravity into the next machine.

' Essentially the same operation takes place in successive machines until the last one in the series is reached.

The action produced in each machine of the serles, therefore, presents a marked contrast to the normal operation of a rotary pulp 4' ing surface, and

screening machine in that in prior machines provision is made for bringing all of the stock which enters the drum into contact with the screening surface, and ejecting from the machine only the tailings with as little good pulp clinging to them as possible. According to the present invention, however, only -a-part of the pulp entering any individual screening drum up to the last one in the series is brought into contact with the screenthe remainder of the pulp furnishes the pressure and thinning fluid required to perform the screening operation efiiciently andto carry the tailings on to the next machine.

The proportion of the stock which is allowed topass through the screening surface of each machine and is taken out of the stream of pulp can be controlled by adjusting the scraper or scoop of that machine, as above described; by regulating the speed of the screening drum so as to vary the centrifugal force, and consequently, the stock elevating effect which it produces; and also by adjusting the weirs in the head box and tailings discharge box so as to produce the desired differential in hydraulic head between the supply and discharge. By withholding a substantial part of the stock from the screen its tendency to thicken is minimized and the unscreened stock leaves the drum in substantially as perfect condition, so far as fibre distribution and consistency are concerned, as when it entered.

It is usually desirable to make the perfo rations or mesh in each succeeding screen somewhat smaller or finer than that in the preceding screen for stock moves from one screen to the next and each screen takes out its portion of fine stock, the coarser materials and dirt become broken one machine to the next the reason that as the up and a finer screen, therefore, is required to keep the dirt out of the fine stock. Also, as the proportion of coarse material in the stock increases it is desirable to decrease the size of the screening perforations.

In a typical arrangement each machine may be allowed to take somewhere between and of the good stock out of the quantity delivered to it, and pass on the remainder to the next machine. Usually the tailings delivered by the last machine in the series will be approximately 2% or 3% of the weight of ered to the first machine. hundred tons of pulp are screened in a days run, the first machine in the series may accept sixty tons and pass along forty tons of stock to the next machine. The second machine may accept twenty tons and reject twenty which will be delivered to the third machine. and discharge eight into the fourth machine, which will accept, say, five or six tons and reject-twoor three as tailings.

This method is particularly effective in grading the good stock delivered by the respective machines. By properly adjusting the machines and regulating the screening conditions, the screened stock discharged from the first machine can be made of a very fine grade and of substantially uniform quality, the tendency for dirt and coarser constituents to pass through the screen of this machine being minimized by the fact that such a large percentage of the good stock is passed along to the second machine and carries the foreign materials with it. The stock delivered by the other machines in the series will correspond more nearly with that which is ordinarily expected from centrifugal machines, but a definite grading of these stocks can be produced by properly selecting the character of the screens and adjusting the factors which affect the screening, as above described.

The invention thus combines the advantages of both the fiat and centrifugal types of screens, producing a grading in quality which is extremely desirable in many mills, while preserving, also, the high capacit of the centrifugal type of screen, and in act increasing this capacity per screen. The power consumption per ton of screened stock also is maintained at a very low figure.

In the system shown in Fig. 1 all of the machines are mounted in the same floor, and the fact that the machines can be located on the same level, the stock being delivered from by the action of the machines themselves and without the use of pumps, is an important practical advantage.

, While I have herein shown a typical embodiment of my invention and have described the process provided by this invention in connection with centrifugal screens of a certaln Assuming that one the original supply of pulp deliv- This machine may accept twelve tons construction, it will be understood that this disclosure has been made rather by way of illustration than limitation, and that the invention may be embodied in other forms without departing from the spirit or scope thereof. Also, that the process may be practiced with other forms of apparatus or machinery. For example, the process can be practiced with the impeller type of centrifugal screen. In some cases, also, the screens which make up the series will not all be of the same construction, 01' even of the same type. The number of machines in the series also will be varied in accordance with the practical requirements of individual installations.

Systems organized in accordance with this invention but using other makes of screens are shown diagrammatically in Figs. 5, 6, 7 and 8. Fig. 5 lllustrates a series of centrifugal machines known commercially as Wells screens connected to operate according to this 1 trated. Thune and spectively, in the invention. Centrifugal screens of the impeller type are used in Fig. 6, the unscreened stock being delivered from one machine to the next by centrifugal pumps. This is not necessary, However, in the other systems illus- Voith screens are used, resystems shown in Figs. 7 1nd 8. For the reasons above stated I prefer, however, to use the type of screen illustrated in Figs. 1 to l. Some changes in the design of the makes of machines shown in Figs. 5 to the changes retained with the materials rejected in each 8 would be required to make them operate at the best advantage in this system, the nature of these changes being obvious fromthe foregoing description and from the character of made in applicants earlier machineto adapt it to this method. d

' Having thus described my invention, what I desire to claim as new is:

1. That improvement in processes 0 of screening pulp, whichconslsts in sub ect1ng a stream-of pulp to a series of centrifugal screening operations in each of-wh1ch a part of the fine stock is taken from said stream while a sufficient proportion of good stock is screening operation to maintain the consistency of the unscreened stock approximately unchanged during the greater part of the process and while the pulp passes from one screening operation to the next.

2. That improvement in processes. of screening pulp, which consists in flowlng a stream of pulp continuously through a serles of screens, performing the screening operation by centrifugal action in each screen, allowing only a part of the good stock in the I stream to pass through the first screen, causing said screen to discharge ahigh percentage of the good stock with the tailings suspended.

in said good stock, and delivering said discharged material to the-next screen in the series.

stream of of the fine stock but 3. That improvement in processes of screening pulp, stream of pulp continuously through'a series of screens, performing the screenlng operation by centrifugal act10n in each screen, permitting a part only of the good stock in the stream to flow through the first screen andthereby to be taken out of the stream, discharging a high percentage of the good stock from said first screen and causing it to pass along to the next screen in the vseries with the tailings suspended in said good stock, and repeating this action in succeeding screens of the series.

4. That improvement in processes of screening pulp, which consists in flowing a pulp continuously through a series of screens, performing the screening operation by centrifugalaction in each screen, taking from said-stream at the first screen only a part of the fine stock and discharging from forty to sixty per cent of the good pulp with the tailings into the second screen, and repeating this action in said second screen.

5. That improvement in processes of screening pulp, which consists in flowing a stream of pulp continuously through a series of screens, performin the screening'operation by centrifugal action in each screen, taking out of said stream at the first screen a part preventing a large proportion of the good stock from flowing through saidfirst screen and causing said proportion of good stock to carry the tailings to. the next screen 'in theseries, and repeating this action in succeeding screens until the last tailings from one screen to the next.

7. That improvement in processes ofscreening pulp, which consists in flowing astream-of pulp continuously through a series 1 of screens, performing the screening operation in successive screens by centrifugal action created screens themselves and against a head of surrounding screened stock, permitting only a part of the fine stock supplied to the first screen to pass through the screen and thereby tobe separated from said stream, and discharging from said first screen a sufficient percentage of good stock with the tailings into the second machine to maintain the stock which consists in flowing a Y through the motion of the tailings to the next screen in -so discharged at substantially the same consistency as the stock delivered to said first screen.

8. That improvement in processes of screening pulp, which consists in flowing a stream of pulp continuously through a series of screens, performmg the screening operation in successive screens by centrifugal action created through the motion of the screens themselves and against a head of surrounding screened stock, flowing the pulp so rapidly past the first screen that only a part of the good stock Will pass through it and be taken out of the stream, discharging a high percentage of the good stock from said first screen with the tailings'into the next succeeding screen, and repeating this action in succeeeding machines of the series.

9. That improvement in processes of screening pulp which consists in subjecting a stream of pulp to a series of centrifugal screening operations in each of which a part of the fine stock is taken from said stream, retaining a suflicient proportion of good stock with the materials rejected by the screens to maintain the consistency of the unscreened stock approximately unchanged as it passes from one screening operation to the next, and utilizing the rotary motion to which the stock is subjected during successive screening operations to deliver the discharged mixture of good stock and tailings to the next succeeding screening operation 0 the series.

10. That improvement in processes of screening pulp, which consists in flowing a stream of pulp continuously through a series of screens, performing the screening operation in successive screens by centrifugal action created through the motion of the screens themselves and against a head of surrounding screened stock, permitting successive screens to take, respectively, from the stream only a part of the fine stock in it and causing them to discharge large proportions of the good stock delivered to them together with the the series, an utilizing the rotary motion created in the stock by each screen to deliver the mixture of good stock and tailings to the next succeeding screen.

11. In a pulp screening system, the combination of a series of centrifugal pulp. screening machines, means for supplying ulp to be screened to the first machine of sai series, and connections for conducting the material discharged from the tailings outlet of each machine to the pulp intake of the next succeeding machine in the series, each of the earlier machines in the series having a relatively 12. In a pulp screening system, the combination of a ser1es of centrifugal pulp screening machines, means for supplying pulp to d the first machines in the series P p large outlet for the unscreened pulp and the tailings rejected by the screen.

of the next sucnation of a series of centrifugal pulp screening machines, means for supplying pulp to be screened to the first machine of said series, and connections for conducting the material discharged from the tailings outlet of each machine to the pulp intake of the next succeeding machine in the series, the screen of the first machine being coarser than those of succeeding machines in said series.

14. In a pulp screening system, the combination of a series of centrifugalpulp screening machines, meansfor supplying pulp to be screened to the first machine of said series, and connections for conducting the material discharged from the tailings outlet of each machine to the pulp intake of the next succeeding machine in the series, the perforations in the screen of each succeeding machine in said series being smaller than those in the preceding machine.

15. In a pulp screening system, the combiing machines; each of said machines including a rotary screening drum, a casing in which said drum is mounted and in which it may be maintained submerged in screened stock means supporting said drum for rapid rotation to create a substantial centrifugal force in the stock closely adjacent thereto, and means for utilizing said rotation to discharge the unscreened stock and tailings from the machine; connections for conducting the material discharged from the tailings outlet of each machine to the pulp intake of the next succeeding machine; and means in each of adjustable to control the proportion of pulp which will be subjected to screening action in its respective machine. and that which will be discharged from the screen with the tailings.

16. In a pulp screening machine, the combination o a screening drum, a casing in which said drum is mounted and in which the drum ma be maintained submerged in screened stoc means for supporting said drum for rapid rotation to create a substantial centrifugal force in the stock closely adjacent thereto, an intake chute for delivering to be screened to the interior of sai drum, a tailings discharge conduit, and an adjustable scoop for acting on the unscreened stock in the machine to conduit. v j

17. In a pulp screening machine, the comdirect it into said I bination of a screening drum, a casing in operation for regulating the discharge of which said drum is mounted and in which the drum ma be maintained submerged in screened stoc means for :supportin said drum for rapid rotation to create a su stantial centrifugal force in the stock closely adjacent thereto, an intake chute for delivering pulp to be screened to the interior of said drum, a tailings discharge conduit, a scoop for acting on the unscreened stock in the drum to direct-it into said tailings conduit, and means operable from outside the casing to adjust said scoop.

18. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, means supporting said drum for rotation, means for conducting pulp to be screened to said drum, a tailings discharge conduit, and means in said casing adjustable while the machine is in tailings from the machine.

19. In a pulp screening machine, the com 1 bmation of a screemng drum, a casing 1n which said drum is mounted, means supporting said drum for rotation, an intake chute for delivering pulp to be screened to the interior of said drum, a tailin'gs discharge conduit, and means for acting on the tailings after they have left the screening surface of the drum to force them into said conduit, said means being adjustable to regulate the discharge of the tailings from the machine.

' ANTON J. HAUG. 

